Plywood over board sheeting

60s house with what i think its original 1x6 sheeting board i have replaced a lot of bad wood mostly around the edges , should i just top the boards with plywood 1/2 inch , and if i do can i just nail the plywood to the existing boards or does it have to be nailed on the rafters ,any input is great fully appreciated .

Through the rafters.
8d ring shank will be just fine.

Break the sheets on and nail to the rafters. We do it quite often,. We always use 10 or 12 d nails to get a good 1 1/2" into the framing.


Great ,thanks for the help